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The Justice Department's inbox was flooded this week by hundreds of thousands of people demanding a federal investigation of the shooting.
NPR's Karen Grisby Bates reports that social media and black media brought this case to wider attention.
KAREN GRIGSBY BATES, BYLINE: Trayvon Martin was shot on February 26, but it was last Friday's release of the 911 tapes from the night of his death that made the dead teen a top story in the mainstream media, and kept him there. This is one of the callers on that tape.
(SOUNDBITE OF A 911 CALL)
UNIDENTIFIED WOMAN #1: I just heard screaming and then a gunshot.
UNIDENTIFIED WOMAN #2: OK, well we have an officer there, did you hear any more gunshots since we've been on the phone?
UNIDENTIFIED WOMAN #1: No, but I don't hear any more screaming either.
BATES: By the end of the evening, 17-year-old Treyvon was dead, shot in the chest by neighborhood watch volunteer George Zimmerman, who told the dispatcher moments before, Martin looked suspicious. When authorities reached Martin's body, they found a can of iced tea and a small bag of candy.
Zimmerman claimed self defense, citing Florida's Stand Your Ground Law. No charges have been filed, and the outrage in black communities across the country was instant. Although the shooting would become national news a few weeks later, the anger immediately flowed through black talk radio, black newspapers and blogs.
(SOUNDBITE OF SONG "TREYVON")
BATES: There was even a song about the incident by rapper Jasiri X, whose "Treyvon" claimed an overzealous Zimmerman jumped to deadly conclusions.
(SOUNDBITE OF MUSIC)
JASIRI X: (Rapping) George Zimmerman, neighborhood block captain, loaded Glock strapped in, fake cop has-been. Got out of the car, ignoring what the cops asked him, they always get away - this time that will not happen.
BATES: Syndicated columnist George Curry says the black media has a long history of highlighting anti-black violence, which mainstream media often picks up on later.
GEORGE CURRY: The black press plays a unique role, because they know right away and can recognize these kinds of stories and the value of them.
BATES: Curry believes that part of the lag between when black and mainstream media began covering the Martin shooting can be accounted for by the communities' different interactions with law enforcement.
CURRY: I think that stems from the fact that whites have a different experience with police than African-Americans and Latinos. To whites, many whites, police are Mr. Friendly. To African-Americans and Latinos, he's Mr. Unfriendly.
BATES: Rashad Robinson is executive director of Color of Change, an online civil rights organization. Color of Change got almost 400,000 signatures forwarded to Attorney General Eric Holder's office in just a few days. Robinson believes this kind of mobilization is important beyond this one case. [POST-BROADCAST CORRECTION: Color of Change received more than 88,000 signatures.]
RASHAD ROBINSON: But also that for that all the Treyvons out there who we may not know yet, that we can start the work of changing our culture to ensure that justice is served, and that folks in power understand that people will not just be quiet when these type of injustices happen.
BATES: Before the Justice Department became involved in the Martin investigation, the Obama White House had been fairly quiet on the subject, other than expressing its condolences and concern. Here's press secretary Jay Carney on Monday afternoon.
JAY CARNEY: Our thoughts and prayers go out to Treyvon Martin's family, but obviously we're not going to wade into a local law enforcement matter.
BATES: A reporter then asked about an earlier, well-known racial confrontation that President Obama stepped in to mediate.
UNIDENTIFIED MAN: You know, the case of Professor Gates up in Cambridge pales compared to this, and the president did speak out about that.
CARNEY: I don't have any conversations to report to you.
BATES: That night, the Justice Department announced it would investigate the Martin shooting.
LAUREN GELLMAN: It becomes harder and harder for politicians to not pay attention.
BATES: Attorney Lauren Gellman specializes in social media issues for the firm blurryedge.com. Gellman says online campaigns by Color of Change and other organizations make a difference.
GELLMAN: It goes from being an issue for just one community, to being a national issue.
BATES: Which is exactly what social media users are counting on in Treyvon Martin's case.
Karen Grigsby Bates, NPR News.